Certain types of vehicles and other enclosures subject to air pressure changes include window arrangements having air disposed within an interspace of the window construction. As air pressure within the vehicle or enclosure decreases, the air within the interspace is drawn out and directed into the body of the enclosure. As pressure increases within the body of the enclosure air therein expands and moves back into the window interspace to equalize pressure. Such transfer of air within the interspace can result in varying levels of absolute humidity within the interspace. If the temperature of the window arrangement is reduced to or below the dew point, then fog and/or frost can rapidly form on panes of the window arrangement.
This problem is particularly evident in aircraft which include numerous windows, each having one or more air cavities which are in fluidic communication with the internal cabin air. These cavities can be delimited by various panes of the window or by a window pane and the inner most window reveal layer arranged most proximate to the passengers. Aircraft window cavities must be vented to the cabin in order to allow for pressure regularization during flight. As the aircraft ascends, cabin pressure reduces, and thus air is vented out of the window cavities in order to stabilize internal air pressure levels. Similarly, when the aircraft descends, cabin pressure increases, and air migrates back into the window cavities. Moisture levels in in cabin air can increase during flight, for example, due to the number of passengers on board, or the use of humidifiers, and/or showers and other bathroom facilities during flight. When this moist air passes back into the window cavities, for example, during a decrease in altitude, fog and/or frost can rapidly form within the window arrangement. This can negatively affect passenger comfort in that views are obscured and can even present a safety hazard when certain flight conditions require clear window visibility.
The occurrence of moisture collection is particularly evident in modern aircraft which have larger windows resulting in larger window cavities that contain an increased volume of potentially moisture laden air. Additionally, these larger modern aircraft windows are often thinner in cross-section, and are thus more sensitive to external temperature. During ascent of the aircraft, these windows cool quickly thus rapidly reaching the dew point, such that traditional moisture control provisions are unable to effectively prevent the development of fog or frost.
Some existing systems involve heating the windows to prevent condensation, while others utilize ant-fog coatings. Heated systems can be high in power consumption, can add unnecessary weight and complexity to the aircraft, and can affect passenger comfort through heat exposure. Anti-fog coatings are newer and hence unproven and limited data is available regarding their reliability. Both of these systems add additional cost to the aircraft.
Thus, a system and a method is required that effectively controls moisture within air cavities of aircraft windows and which is simple, lightweight, low cost, easy to maintain, and does not disturb the comfort of passengers.